The present invention, generally relates to roller skates. More specifically, the present invention relates to in-line roller skates, to molds for making in-line skates and to a method of molding in-line skates. The present invention also relates to a molded boot with a mechanism for securing laces.
In-line roller skates generally include a boot, a frame attached to the boot, and in-line wheels rotatably attached to the frame. The boot often includes a shell section and a cuff section which is pivotally connected to the shell section. Some in-line skates include braking mechanisms which are typically attached to the frame.
The boot and frame are traditionally manufactured as separate pieces such that the frame is attached to the sole of the boot after manufacture of the frame and boot. The frame is commonly attached to the boot with rivets, though other fastening mechanisms are also used.
Separate manufacture of the boot and frame with later attachment of the frame to the boot presents challenging design, manufacture, and quality control problems. One set of problems arises where the rivets or other fasteners protrude inside the boot. The protruding rivets or fasteners often require added padding to shield skaters' feet from injury or discomfort.
Another set of problems concerns proper positioning of the frame relative to the boot. Proper alignment of the frame and the boot is necessary to insure optimum skate performance and comfort. The possibility for misalignment of the frame and boot is inherent in the acts of positioning the frame relative to the boot and fixing the frame to the boot. Also, longterm, secure attachment of the boot and the frame is critical. Otherwise skate performance may suffer and the skater may risk physical injury. Skates with boots and frames which are not firmly attached or are out of alignment are of little value to a skater.
It is desirable to avoid the listed problems related to separate boot and frame manufacture and assembly. Potential techniques for avoiding the problems include combined manufacture of the boot and frame as a single piece unit. One form of combined manufacture includes integrated molding of the boot and frame. The ULTRA-WHEELS.RTM. Zephyr model skate, manufactured by Koflach Sportgerate Gesellschaft of Graz, Austria, is an example of an in-line skate with an integrally molded boot and frame. Integrated molding may avoid fastener protrusion inside the boot, assembly alignment problems, and difficulties in attaining secure attachment.
Though it is desirable to mold the boot and frame as an integral unit, integrated molding may include a variety of problems. For example, integrated molding of the frame and boot typically creates differential shrinkage problems such as sink marks, warping, and molded-in stress. N. G. McCrum, C. P. Buckley & C. B. Bucknail, Principles of Polymer Engineering 337 (1988). Beyond aesthetic concerns, differential shrinkage may weaken the integrally molded skate, may cause misalignment of the skate frame walls, or may prevent all of the skate wheels from simultaneously contacting a level ground surface. Additionally, development of sink marks in the sole of the boot during manufacture may cause the skater discomfort while wearing the skate. Poor or undependable skate performance may also result from differential shrinkage.
Skates with integrally molded frames and boots discourage resort to some potential techniques for minimizing the effects of differential shrinkage. For example, it is undesirable to decrease the thickness of portions of the sole using mold core pins. Added core pins require addition of padding in the sole for skater comfort and may increase the difficulty of removing the integrally molded boot and frame from the mold core. Also, strengthening the frame by including honeycomb reinforcement along interior sides of the frame walls is problematic. Such honeycomb reinforcement creates substantial mold design problems and may increase the difficulty of removing the integrally molded boot and frame from the mold core. Another potential solution, increasing the size of the fillets at the junction of the frame walls with the boot sole, may enhance rather than minimize the effects of differential shrinkage. Additionally, larger fillets may increase the weight of the boot and, considering other desirable features, may complicate skate design and molding.
Though in-line skates with integrally molded boot and frame are desirable, integral molding of the frame and boot is a potential source of design manufacture, comfort, performance, and aesthetic problems. Integral molding of in-line skates includes issues of differential shrinkage and issues of limitations upon techniques for avoiding or minimizing undesirable effects of differential shrinkage.
Another point of concern of in-line skates in particular and footwear in general involves eyelets. In footwear, eyelets are commonly used to line the lace holes. Eyelet use is sometimes beneficial, such as when eyelets line lace holes of footwear made of soft material. In this application, the eyelets help prevent the laces from tearing the soft material. However, eyelets are not always beneficial. For example, the knurled portion of eyelets may have sharp edges which aggravate lace wear. These sharp edges often contribute to premature lace breakage.
Eyelets may also cause problems when used with hardened shells of footwear made of certain molding resins. Hardened shells are not generally conducive to secure eyelet attachment. Even minimal variations in the wall thickness of hardened shells may cause uneven eyelet attachment and consequent failure of eyelets. Eyelets which cannot be effectively attached to a molded in-line skate are of diminished value to the manufacturer and the skater. One solution to the eyelet attachment problem is to use softer materials which will better accept eyelets. This solution is unsatisfactory to those who want or require the features of hardened shells of particular molding resins.
Molding resins which cure into hardened finished materials are frequently desired molding components for in-line skates. Harder materials are typically more durable and often last longer than softer materials under certain conditions. Additionally, harder materials may enhance safety in properly designed skates. Skates made of harder materials may shield the skater from contact with objects and obstructions and may decrease risk of injury in the event of collision.
Another point of concern of in-line skates involves pivoting movement of cuffs about boots. Cuffs are sometimes pivotally attached to boots of in-line skates to provide lateral ankle support. Boots with pivoting cuffs may include movement-related problems, particularly where the cuffs and boots are made of harder materials. For example, depending upon the design of the boot, the cuff may hang up on the rear portion of the boot as the cuff pivots rearward. Collapse or other failure of the boot may also occur when the cuff pivots relative to the boot. Safety and performance considerations make cuff hang up and boot failure undesirable features for in-line skates.